Beryllium Target studies for Long Baseline Neutrino Experiment - - PowerPoint PPT Presentation

Beryllium Target studies for Long Baseline Neutrino Experiment (LBNE) at 0.7 MW and 2 MW operation

• RAL High Power Targets Group: Chris Densham, Otto

Caretta, Tristan Davenne, Mike Fitton, Peter Loveridge, Matt Rooney

• In collaboration with Fermilab: Patrick Hurh, Bob

Zwaska, James Hylen, Sam Childress, Vaia Papadimitriou

Beam Parameters used in study

Proton Beam Energy (GeV) Protons per Spill Repetition Period (sec) Proton Beam Power (MW) Beam sigma, (mm) 120 4.8 e13 1.33 0.7 1.5 – 3.5 60 5.5 e13 0.76 0.7 1.5 – 3.5 120 1.6e14 1.33 2.3 1.5 - 3.5 60 1.6e14 0.76 2 1.5 - 3.5 Bunch length (nano-sec) Bunch spacing (nano-sec) Bunches per Pulse Protons per Bunch Pulse length (micro-sec) 2-5 18.8 519 3.1e11 9.78

Assumptions for target technology options

1. Target length = 1m, Target diameter between 9mm and 21mm 2. Low z target material

– lower heat load per pion produced – lower production of neutrons and other secondary particles – less secondary heating and radiation damage to horn and target station components

3. Candidate materials

• Baseline: graphite, water cooled (IHEP study)
• Alternative materials for this study: Be and alloys

(motivated by radiation damage of graphite) 4. Geometry options:

• Target integral with horn inner conductor (water spray cooled)
• Separate target and horn inner conductor cooled by:

– Water – 2-phase water – Helium – Air

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 1.75 2.25 2.75 3.25 3.75 4.25 4.75 5.25 5.75 6.25 6.75 7.25 7.75 8.25 8.75 9.25 9.75 10.25 10.75 11.25 11.75 yield [pions/proton] pion energy [GeV]

yield in energy range of interest

total = 1.43 pions/proton

FLUKA studies ‘Figure of Merit’

– The ‘Figure of Merit’ is a convolution of the selected pion energy histogram by a weighting function:

• 1.5 GeV < E < 12 GeV
• pT <0.4 GeV/c

– Weighting function W = E2.5 compensates for low abundance of most useful (higher energy) pions – Devised by R.Zwaska (FNAL) – Implemented in FLUKA by Tristan Davenne

100 110 120 130 140 150 2 4 6 8 10 12 FoM [pions+/-/proton * GeV^2.5] target radius [mm]

Change in FoM with target radius

beam sigma=3.5mm beam sigma=1.5mm large target design radius = 3sigma small target design radius = 3sigma

Figure of Merit as a design guide

Investigate:

• ptimum target radius

sensitivity to off centre beam target length beam energy (60 vs 120GeV) etc etc

50 60 70 80 90 100 110 120 130 140 150 1 2 3 4 5 6 7 8 9 10 11 12 FoM [pions+/-/proton * GeV^2.5] parallel off centre deviation [mm]

performance drop off with eccentric beam

1.5mm 3.5mm

60 80 100 120 140 160 180 80 120 160 200 240 280 320 360 400 FOM Target length [cm]

FOM vs length

10.5mm radius cylinder 10.5mm radius spheres 4.5mm radius cylinder (low statistics)

Energy deposition contour plots

Energy deposition in beryllium target (GeV/cc/proton) Beam energy = 60 GeV Beam sigma = 3.5mm sigma Target radius = 10.5mm Target length = 1 m Integrated energy deposition = 16.9kJ/spill 15% increase in integrated energy deposition with magnetic field Effect of horn focussing of secondary particles

target radius

Effect of water and horn inner conductor on FoM

20 40 60 80 100 120 140 160 120GeV 1.5mm 120GeV 3.5mm 60GeV 1.5mm 60GeV 3.5mm FoM [pions+/-/proton * GeV^2.5]

Reduction in yield due to water jacket

Target Water jacket

4% reduction in FoM due to presence of water Significant reduction in FoM due to inncer conductor being in close proximity with target

Stress Calculations

Beam Energy (GeV) Beam Power (MW) Beam sigma (mm) Peak “total” stress (AUTODYN) [MPa] “Quasi-static” thermal stress component (ANSYS) [MPa] “Stress-wave” inertial component (inferred through subtraction) [MPa] 120 0.7 1.5 177 100 77 3.5 55* 27 28 120 2.3 1.5 575* 334 241 3.5 180 90 90

Stress Levels exceeding design stress for some design options

• Significant

Longitudinal Stress Waves

Effects of accidental 2σ off-centre beam on integrated target & horn inner conductor

Otto Caretta

Target segmentation

• Segmenting reduces inertial stress by

reducing target expansion time

• Also removes problem of an off-centre

beam inducing vibration modes

• Spheres avoid stress concentrations

associated with corners

Effects of accidental 2σ off-centre beam on stress waves in simply supported target rod

100 200 300 400 500 600 700 800 5 10 15 20 25 Peak Von-mises stress as a result of 2sigma off centre beam [MPa] Diameter of cylinder or sphere [mm]

Peak stress with off centre beam

0.7MW spheres 2.3 Mw spheres 0.7 MW cylinder 2.3 MW cylinder nominal yield strength and endurance limit for beryllium Max design stress (as specified by Fermilab)

Limited range

• f design

parameters fall below design stress

Physics vs Engineering Optimisation ? Target and Beam Dimensions

• For pion yield – smaller is better

– Maximum production and minimum absorption (shown by FoM)

• For target lifetime – larger diameter and shorter length is better

– Lower power density – lower temperatures, lower stresses – Lower radiation damage density

• For integrated neutrino flux, need to take both neutrino flux and

lifetime factors into account

– Want to make an assessment of trade off between target lifetime vs beam and target dimensions – Answer will depend on Target Station engineering (time to change

• ver target and horn systems)

Combined target and horn inner conductor

Combined target and horn inner conductor

• Analysis procedure (Peter Loveridge)

Thermal Transient

ANSYS (3D slice)

emag

Transient ANSYS (3D slice)

Current pulse definition Magnetic field Outputs: Model: Inputs: Software: Current density Joule heating Lorentz force Resistive heat generation rates Temperature distribution

Structural Static

Static stress / strain Nodal forces Nodal temperatures

ANSYS (3D slice)

Energy density distribution

Energy Deposition

Proton beam parameters

FLUKA (3D)

Beam heat generation rates

Magnetic modelling

B F I

Peter Loveridge         

1 2 2

ln 4 R R I Flong  

Longitudinal force in inner conductor

0 A/mm2 1200 A/mm2 0 Tesla 5.6 Tesla 0 MPa 129 MPa 300 K 311 K

Max current density

• Max. magnetic field
• Max. Lorentz stress
• Max. temperature

Solid beryllium inner conductor diameter = 21mm

Combined effects of: 1 ms 300 kA current pulse + 2.3 MW 120 GeV beam pulse

Ø21mm Beryllium Combined Target / Conductor Beam Heat + Joule Heat + Lorentz Force

300 310 320 330 340 350 360 370 380 0.0 0.5 1.0 1.5 2.0 Time [msec] Temperature [K] 20 40 60 80 100 120 140 160 Von-Mises Stress [MPa]

• Min. Temperature
• Max. Temperature
• Max. VM-Stress

Conclusions on combined target/horn IC

• Complex, combined horn current pulse and beam pulse

effects

• Need to reduce longitudinal Lorentz stresses requires

target diameter to be larger than desired for

• ptimum pion yield
• At 2.3MW target segmentation required so can’t use

target as a conductor

• Recommend looking at longitudinally segmented target

separate from horn

Advantages & disadvantages of different cooling methods

Advantages Disadvantages

Water spray cooling

 High heat transfer  No shock issues  Experience for horn cooling  Good for integrated target/horn  Not compatible with separate target & horn  Patchy/non uniform cooling  Reliability of nozzles  Tritium production  Dissociation of water

Water forced convection cooling

 Uniform cooling  High heat transfer  Simple hardware requirements  Low temperature rise of water  Shock/water hammer issues  Heat deposition in water  Tritium production  Dissociation of water

Helium cooling forced convection

 Uniform cooling  No shock issues  Low radiation  Lower density than water  High pressures required to reduce pressure drop and obtain sufficient mass flow

Air cooling forced convection

 Simple hardware requirements  Uniform cooling  Low cost  Can exhaust cooling air into target station  Non re-circulating system, no activation of compressor  Lower density than water  Most attractive for low beam powers  Consequences of NOx production and other radiochemistry effects

LBNE target study: conclusions for 2 – 2.3 MW

• Combined target/horn inner conductor

– Not recommended as dimensions dominated by horn current pulse Lorentz forces rather than pion production

• Candidate beryllium target technologies for further

study:

1. Water cooled longitudinally segmented 2. Pressurised helium cooled separate spheres

• Further recommendation for 0.7 MW operation

– Air cooled target appears an attractive option for LBNE target station configuration

Water cooled target concept (2.3 MW)

NB stress waves in water (need helium bubble population?) Mike Fitton

Water cooled target concept (2.3 MW)

Mike Fitton

Pressure drop vs flow rate Target core temperature vs flow rate

ΔT=29K ΔT=5.7K

Direct water cooling – secondary heating of water surrounding 10.5 mm radius beryllium target

Pressure rise calculated from constant volume assumption (conservative) i.e. Bulk Modulus and Thermal Expansion Coefficient depend on water temperature

T K P

V 

  

Pressurised helium cooled concept (2.3 MW)

• Be sphere diameter

= 13 mm

• Helium outlet pressure

= 10 bar

• NB 0.7 MW possibility

using air discharging at atmospheric pressure Otto Caretta & Tristan Davenne Mid-plane temperatures

Single-pass air cooled concept (700kW)

Atmospheric pressure air cooled system looks reasonable for 700kW Mike Fitton